A problem not sufficiently addressed by the prior art is the fluoride and unwanted trace material content included in the shell, carapace and crust of crustaceans. In the disclosure infra the notion “krill” is used, signifying that krill is one hind of crustaceans wherein this problem is especially accentuated, but also other types of crustaceans are relevant in the present invention. Another problem related to krill, and especially the Antarctic krill, is the high content of polar lipids during the second half of the fishing season.
As mentioned a well known problem when processing Antarctic krill (Euphausia superba) is that the lipid content, and especially the polar lipid content such as phospholipids, can be very high during the second half of the season from April/May to June/July.
As a rule for most known animal species the content of polar lipids, such as phospholipids, is nearly constant and variations in total lipid content is caused by variations in the content of neutral lipids such as triglycerides. Despite these very high variations of lipid content, the ratio between triglycerides and phospholipids is nearly constant for the Antarctic krill. It is also well known that lipids, and especially phospholipids, cause strong emulsions. Such emulsions cause problems in the separation of the fractions in the processes, such as hydrolysis, which involves separation of lipid- and proteinaceous fractions. The developed process according to the present invention also solves the emulsion problems by creating an aggregate of non-soluble proteins and phospholipids before and during the last separation step in the process.
Krill represent a vast resource for biological material. The amount of Antarctic krill (Euphausia superba) which live in the Antarctic Ocean, although varying depend on the calculation method and investigation, is roughly 1 to 2×109 tons and the possible weight of catch is estimated at 5 to 7×106 tons. These small crustaceans that live in the cold waters around the Antarctic, are interesting as a source for proteins, lipids such as phospholipids, poly-unsaturated fatty acids etc., chitin/chitosan, astaxanthin and other carotenoids, enzymes and other materials, and several methods for isolating such materials have been developed.
The background for the present invention resides in the circumstance that krill accumulate fluoride in their shell, increasing the fluoride amount of any produced material either through the inclusion of such shell parts, through extraction processes not taking into account the transfer of fluoride to the final material through the extraction steps or through time-consuming processes wherein free fluoride or loosely bound fluoride may diffuse from the shell material and into the further processed material, making the end product high in fluoride ions or fluorinated compounds.
Fluoride is a compound that in high concentrations is detrimental for the health of land-dwelling animals as well as all kind of fish and crustaceans and especially fresh-water fish species, since fluoride atoms have the tendency of entering into the bone structure of such organisms and creating fluorosis (a weakening of the bone structure similar in its effect to osteoporosis, but different since it is the bone structure itself, and not the porosity of the bone that is affected). Skeletal fluorosis is a condition characterised by skeletal abnormalities and joint pain. It is caused by pathological bone formation due to the mitogenic action of fluoride on osteoblasts. In its more severe forms, skeletal fluorosis causes kyphosis, crippling and invalidism. Secondary neurological complications in the form of myelopathy, with or without radiculopathy, may also so occur. High fluoride intake has also been shown to be toxic to the male reproductive system in rat experiments, and in humans high fluoride intake and symptoms of skeletal fluorosis have been associated with decreased serum testosterone levels.
Consequently, if krill material is to be used as a starting material for food or feed products, precautions have to be taken for removing fluoride through the processing steps. However, the diffusion of fluoride and the presence of miniscule krill shell material represent a problem that is most difficult to overcome when processing krill material in an industrial scale.
Additionally it can be advantageous to reduce the ash content including trace elements from the proteinaceous material produced from the catch.
Thus there exists a need for an industrial method producing proteinaceous materials and lipids from krill wherein fluoride is cost-effectively removed for producing products with significantly reduced fluoride content.
Polar lipids such as phospholipids are essential for cell membranes and are also called membrane lipids. Normally the total lipid content in fish and other aquatic and terrestrial animals varies due to variations in feed accessibility through the year. The variations is normally caused by variations in the content of non polar lipids in the organisms which is stored and used as energy reserves during periods of low or no access to feed, while the content of phospholipids is relatively constant. However, for Antarctic krill this is different because the relative content of triglycerides and phospholipids remains almost constant also when the fat content in this species varies from 2% up to 10% during the fishing/harvesting season. This means that the phospholipid content in raw Antarctic krill can be up to 5%. Lipids, and especially polar lipids as phospholipids, are known to create strong emulsions in industrial processing according to prior art which involves heating-, stirring- and separation steps such as a hydrolysis process. This emulsion will normally cause problems in separating the lipid- and protein fractions.
Thus there also exists a need for an industrial method for elimination of separation problems caused by emulsion when producing proteinaceous concentrates from krill.
There also is a need for a versatile industrial method addressing both the removal of fluorine from the processed krill material and the varying contents of polar lipids in the krill material.